Gas oven carbon monoxide

[Linda Swearingen]

It seems like gas ovens all discharge carbon monoxide (except the ones with automatic vent fans to the outside, which isn't many). Is there any sort of industry standard as to how much is too much? I realize that they can't burn 100% until they warm up some, but I've seen some that don't back down to under 8 or 10 ppm, and a few that were so high (200+ppm) that they are absolutely unsafe to operate as they are. But where do we draw the line?

[John Dirks Jr]

I always recommend that CO detectors be installed whenever any fossil fuels are used in a home.

If for whatever reason the CO levels get high enough to present a hazard, the alarm should warn the occupants.

.

[Bob Harper]

ANSI Stds. allowd for up to 800ppm from gas ovens. Any you just thought it was the tryptophan from the turkey making you sleepy at Thanksgiving.....

John, the operative words in your post were "should" warn and "high enough to present a hazard".

Present stock off the shelf CO alarms listed to UL 2034 are proven unreliable at best. So much for the *should* part. They are designed to ignore levels under 70ppm leaving you exposed. They even state on their packaging if you are elderly, have small infants or children or certain medical conditions, you may need "additional protection". So why am I buying this piece of junk in the first place?

There are two low level CO monitors on the market that are reliable and provide adequate protection, thus they are NOT listed to UL 2034 for single station monitors or UL 2075 for central station monitoring (which use the same alert levels): The CO Experts and the NSI 3000.

Try this test: crack the door to the oven then set to 'broil' and monitor CO. All that cool room air rushing into the top of the heat spreader plate will cool the gases causing CO formation. You can also demonstrate the effects on a range top with a pot of cold water.

yes, ovens and ranges *should* be ventilated but unfortunately they don't *have* to be.

Bob

[DavidR]

yes, ovens and ranges *should* be ventilated but unfortunately they don't *have* to be.

Bob

They should be banned IMHO.

No place for them in any type of construction anymore.

[Gunnar Alquist]

They should be banned IMHO. No place for them in any type of construction anymore.

David,

Ummm... ovens and ranges? How are we supposed to cook? ;)

[DavidR]

David,

Ummm... ovens and ranges? How are we supposed to cook? ;)


I get by just fine on electric. :D

[Rick Hurst]

A true Chef or someone who really enjoys cooking knows that gas is the only way to cook.:p

rick

[Gunnar Alquist]

A true Chef or someone who really enjoys cooking knows that gas is the only way to cook.:p

Right On! Ban the electric wimps! :cool:

[Dennis Krouse]

Thank you Rick and Gunnar. I couldn't agree more!

[Rick Cantrell]

Bob
It has been years since I read up on CO detectors, so my opinions are likely to be out of date.
My understanding of CO detectors is that they are unreliable, and pretty much useless in the home, even the professionally installed type that I have access to. I don't recommend them.
You said "There are two low level CO monitors on the market that are reliable and provide adequate protection".
Which two?

Thanks

[DavidR]

So you guys that use gas have made sure your ovens are operating safely and have low level CO monitors installed?

If they are vented and operating safely not a problem, otherwise I fail to see why you would want one in a building.

A real chef uses an open flame but I don't bring that inside either. :p :D

[Bob Harper]

Bob
It has been years since I read up on CO detectors, so my opinions are likely to be out of date.
My understanding of CO detectors is that they are unreliable, and pretty much useless in the home, even the professionally installed type that I have access to. I don't recommend them.
You said "There are two low level CO monitors on the market that are reliable and provide adequate protection".
Which two?

Thanks

Rick, finish my sentence. Both I refer to ARE very reliable, unlike the listed alarms and they do alert at low levels unlike listed alarms. The NSI 3000 is available only if you take Day 1 of the NCI Co & Combustion Course. You can buy the CO Experts online from George Kerr.

Guys, understand where DavidR is coming from. Aside from teaching the NCI CO & Combustion course, he is a practicing professional HVAC tech who does check gas ovens so he knows first hand what he's talking about. I've tested a few dozen and found CO issues to one degree or another with all. Understand the ventilation is needed on electric ranges and ovens as well. The aerosolized food particles and humidity should be exhausted to the outdoors regardless of fuel burned.

Those professional chefs cook over professional ovens and ranges with massive exhaust fans rated in the thousands of CFMs sucking that kitchen inside-out. Ever tried to open a door to a commercial kitchen? Some of the worse depressurized spaces in the world. I've had commercial kitchen fans affect direct vent gas fireplaces. Had to install a $10K makeup air system.

The lack of a proper interlock with the gas burner was a direct cause of a CO poisoning event near me that sent people to the ER twice from the same grocery store caused by the same bake oven. What saved the day was the personal CO monitor/ alarm carried by the paramedics who responded to an old lady collapsed at the bake counter. It went off at 35ppm. I have carried a personal CO monitor for years and it has alerted me to hazardous environments, including being in traffic. How do you know you are not walking into a toxic environment every day? You guys should be wearing a personal 4 in 1 alarm: % LEL, CO, O2, H2S. That's what my next personal alarm will be.

Bob

Bob

[JORY LANNES]

Great subject however I think a bigger question needs to be asked. HOW MANY INSPECTORS CHECK FO CO LEVELS?

In a informal study of my ASHI chapter less than 50% of the members check for carbon monoxide as part of there standard inspection.

Testing for CO is not an Illinois or ASHI standard of practice.

I have found over the years several unsafe hot water heaters and furnaces only because of my CO tester.

Should the SOP be changed?

[Rick Cantrell]

"Rick, finish my sentence. Both I refer to..."
Sorry Bob, I was reading it wrong. When you said CO Experts I thought that meant, people that are carbon monoxide experts in general and NSI3000 was a standard.
Thanks for clearing that up.

[DavidR]

Great subject however I think a bigger question needs to be asked. HOW MANY INSPECTORS CHECK FO CO LEVELS?

In a informal study of my ASHI chapter less than 50% of the members check for carbon monoxide as part of there standard inspection.

Testing for CO is not an Illinois or ASHI standard of practice.

I have found over the years several unsafe hot water heaters and furnaces only because of my CO tester.

Should the SOP be changed?

Yes the SOP should be changed Jory, kudos to you for being proactive and testing without being made to!

You're setting a good example for those in your chapter that aren't aware of what they could be walking into.

[DavidR]

Rick, finish my sentence. Both I refer to ARE very reliable, unlike the listed alarms and they do alert at low levels unlike listed alarms. The NSI 3000 is available only if you take Day 1 of the NCI Co & Combustion Course. You can buy the CO Experts online from George Kerr.

Guys, understand where DavidR is coming from. Aside from teaching the NCI CO & Combustion course, he is a practicing professional HVAC tech who does check gas ovens so he knows first hand what he's talking about. I've tested a few dozen and found CO issues to one degree or another with all. Understand the ventilation is needed on electric ranges and ovens as well. The aerosolized food particles and humidity should be exhausted to the outdoors regardless of fuel burned.

Those professional chefs cook over professional ovens and ranges with massive exhaust fans rated in the thousands of CFMs sucking that kitchen inside-out. Ever tried to open a door to a commercial kitchen? Some of the worse depressurized spaces in the world. I've had commercial kitchen fans affect direct vent gas fireplaces. Had to install a $10K makeup air system.

The lack of a proper interlock with the gas burner was a direct cause of a CO poisoning event near me that sent people to the ER twice from the same grocery store caused by the same bake oven. What saved the day was the personal CO monitor/ alarm carried by the paramedics who responded to an old lady collapsed at the bake counter. It went off at 35ppm. I have carried a personal CO monitor for years and it has alerted me to hazardous environments, including being in traffic. How do you know you are not walking into a toxic environment every day? You guys should be wearing a personal 4 in 1 alarm: % LEL, CO, O2, H2S. That's what my next personal alarm will be.

Bob

Bob


I really like the idea of the 4 in 1 Bob, Christmas might come early. :D

The other item with commercial kitchens and the pressure imbalances due to improperly balanced hoods is the effect they have on the water heaters sitting in those very kitchens.

Many kitchen fires and CO poisonings have been attributed to this depressurization.

[Bob Harper]

Just another example why you should wear a 4 in 1 monitor: BREAKING NEWS !!!! - Two badly burned in gas explosion - Carmi, IL - The Carmi Times (http://www.carmitimes.com/news/x1137934248/BREAKING-NEWS-Two-badly-burned-in-gas-explosion)

This was two HVAC techs who were injured. One is a grizzled veteran and friend of a frequent contributor over on HVAC-Talk.com where I found this. There was an LP tank in the yard to a furnace in the crawl space. He thought he had the tank shut off. No shutoff within 6ft. of appliance (now you know why code requires this). They went under to service and light pilot. 3rd degree burns on face and hands but they think he will live. They did not smell the gas so they ASSumed they were ok. Either the gas was below their noses or it was a case of 'odor fade'. Regardless, a 4 in 1 set to alert at 20% of the LEL could have warned them of the hazardous environment where they could have escaped unhurt. BTW, for LP gas, the LEL is about 4,300 ppm.

If there is a venting problem to where CO2 is being released into the room it will displace the O2 so an oxygen deficient space is a problem for people and combustion.

With all the busted stink pipes/ traps in basements and the low IDLH & PEL for hydrogen sulphide, this is cheap protection.

Bob

[John Dirks Jr]

So, who believes it's a bad idea to recommend CO detectors/alarms?

[Dennis Krouse]

So why were they trying to light the pilot if they thought the tank was off???

[JORY LANNES]

What is a personal 4 in 1 alarm: % LEL, CO, O2, H2S.? Who is the manufacture,where are they sold, approx price?

Thanks

Jory

[mathew stouffer]

Well said Rick, gas is king.

[DavidR]

None of you guys that are for the Kevorkian cooking style have said if you've tested your gas ranges yet.

[Bob Harper]

What is a personal 4 in 1 alarm: % LEL, CO, O2, H2S.? Who is the manufacture,where are they sold, approx price?

Thanks

Jory

Jory, if you Google personal carbon monoxide alarms, you will get tons of hits. You can check with sites that service the Fire Service and Home Inspector equipment suppliers. Another search parameter is "confined space entry".

What these do is sniff for combustible gases within 20% of the Lower Explosive Limit, carbon monoxide, low oxygen, and hydrogen sulphide. May alert you to hazard and allow sufficient time to egree before being overcome and make the headlines tomorrow.

prices can range from a few hundred dollars to a lot of hundreds of dollars. Just have to ask yourself what is your life worth?

Let's say you go basement or crawl space spelunking while the Realtor and buyer wait in the kitchen. You fail to show for for an hour so they start calling out for you. Meanwhile, you've been dead for 55 minutes.

Bob

[Ken Rowe]

A new law went on the books in Minnesota last year requiring carbon monoxide detectors in all single family homes within 10 feet of each bedroom. Not just new construction, all homes. In fact, even if the house has no gas supply to it...they're still required.

All of us with my company check carbon monoxide levels of gas appliances. I used to only check water heaters and heating systems until one day I got of reading of 110 ppm in a the basement when neither the furnace nor water heater were operating. I tracked it down to the pilot light of an old gas stove hooked up in the basement. Over 400 ppm at top of the stove, without the burners being lit. I check all gas appliances now.

[DavidR]

Just another reason to test these time bombs.

Electrolux ICON and Kenmore PRO Gas Ranges Recalled: Carbon Monoxide Poisoning (http://www.usrecallnews.com/2009/11/cpsc-7703.html)

Just remember it might not be the turkey making you sleepy.

Happy Thanksgiving guys.

[Dennis Krouse]

None of you guys that are for the Kevorkian cooking style have said if you've tested your gas ranges yet.
As a gas accident investigator how come no one mentions that there are FAR more deaths and fires contributed to electrical causes???

[Jerry Peck]

contributed to electrical causes???

Possibly because when there is no other defined cause the default goes to 'possibly electrical in origin' instead of anything else. Which simply means 'cause undetermined' but it is marked down as 'electrical'.

I have read many reports and discussions that, when a cause cannot be determined, and unless there is *NO* electrical power to a structure, the default cause is usually chosen to be 'possibly electrical in origin', which creates the illusion that there are more electrical fires than there really are.

[Bob Harper]

Dennis, what is the mechanism for capturing ACTUAL carbon monoxide incidents? ---ONLY when someone suspects CO and an agency such as the Fire Dept. reports it to where it gets picked up by the CPSC. Now, how many elderly die from "natural causes" where a carboxyhemoglobin level is recorded immediately post mortem to rule out CO? That's just an example of CO related deaths.

Now, what about all those non-fatal incidents where people get exposed and suffer ill effects? How many people suffer from "allergies", "flu", "mental disorders", "sick house syndrome" and other maladies that are improperly diagnosed and there is no proper correlation with the indoor environment? I can tell you that many, many thousands of Americans are exposed to lower levels of CO daily and nothing is being done about it. Since the reporting mechanisms are not in place, word is not getting out. A few of us such as DavidR and myself do what we can locally but we are a few fish in a sea.

Bob

[Bob Elliott]

A new law went on the books in Minnesota last year requiring carbon monoxide detectors in all single family homes within 10 feet of each bedroom. Not just new construction, all homes. In fact, even if the house has no gas supply to it...they're still required.

All of us with my company check carbon monoxide levels of gas appliances. I used to only check water heaters and heating systems until one day I got of reading of 110 ppm in a the basement when neither the furnace nor water heater were operating. I tracked it down to the pilot light of an old gas stove hooked up in the basement. Over 400 ppm at top of the stove, without the burners being lit. I check all gas appliances now.

Let me get this straight....
Minnesota Requires detectors 10 feet from bedrooms which is very lax and in Chicago (Illinois) we have the same lax law as CPSC recommends inside the bedroom.

Sleep with the door closed and you wake up dead I say.

But then they have the goofy idea you need a detector for CO even with no gas???

Here we do not even require them if there is gas, when a Boiler is in the basement and a apartment unit is say on the 10th floor.

To address the rest of this thread if Stoves are so dangerous we should all be Dead..HA ha.

I think if there is danger it is from being in a tight house with the thing on all day.

I would be more concerned with checking for gas leaks and do not pull out my TIFF to give a show as my Sniff does fine.

Tiff is good to pinpoint.

[Bob Harper]

Bob, your sarcasm does not make up for your lack of scientific basis. Let me address just a few of your quips:
Whether 10 from a bedroom or inside a bedroom, it matters much more what kind of CO alarm you are using. If you are relying on alarms listed to UL 2034 or 2075, you are still at risk irregardless of placement. Learn about low level CO hazards and low level UNlisted CO monitors.

The *goofy* idea even if no gas is because of all the other sources of CO poisoning such as car exhaust and gasoline generators run indoors. Minn. had several deaths from gasoline generators used indoors during winter storms. Yes, you would think they would get it but they don't. Even with the CO warnings now required by the CPSC on generators, people still run them indoors. When it's cold, they get desperate. They will burn a gas oven for heat when the electricity is off. I transported victims of this back when I was a paramedic. They did a study in Minn. demonstrating that to warm your car you must pull it out of the attached garage and close the door or else CO will entrain indoors. You can get CO poisoning in a total electric home from garages, hibachi grilles, fireplaces, and BBQ grilles too close to an indoor opening. Not very goofy to me.

CO is lighter than air and, along with stack effect, will rise to the upper floors, esp. in very tall buildings. You ought to read the case on "A Suicide in Sendai" in Japan. BTW, do those 10 story apartment buildings have garages underneath?

The listing on a gas oven is based upon a limited burn rate of no more than 4 hours within an 8 hour period combined with adequate ventilation. FYI, gas ovens DO make people sick. They don't have to kill to be a problem.

FYI, a TIFF 8800a is sensitive to methane only down to 500 ppm so it is not very useful for finding low level gas leaks and is cross-sensitive to about 30 common household compounds that can give false positives.

Perhaps if you took the NCI Carbon Monoxide and Combustion Certification Course you wouldn't be so cavalier with your responses.

Have a nice day,
Bob H.

[Bob Elliott]

Bob, your sarcasm does not make up for your lack of scientific basis. Let me address just a few of your quips:
Whether 10 from a bedroom or inside a bedroom, it matters much more what kind of CO alarm you are using. If you are relying on alarms listed to UL 2034 or 2075, you are still at risk irregardless of placement. Learn about low level CO hazards and low level UNlisted CO monitors.

The *goofy* idea even if no gas is because of all the other sources of CO poisoning such as car exhaust and gasoline generators run indoors. Minn. had several deaths from gasoline generators used indoors during winter storms. Yes, you would think they would get it but they don't. Even with the CO warnings now required by the CPSC on generators, people still run them indoors. When it's cold, they get desperate. They will burn a gas oven for heat when the electricity is off. I transported victims of this back when I was a paramedic. They did a study in Minn. demonstrating that to warm your car you must pull it out of the attached garage and close the door or else CO will entrain indoors. You can get CO poisoning in a total electric home from garages, hibachi grilles, fireplaces, and BBQ grilles too close to an indoor opening. Not very goofy to me.

CO is lighter than air and, along with stack effect, will rise to the upper floors, esp. in very tall buildings. You ought to read the case on "A Suicide in Sendai" in Japan. BTW, do those 10 story apartment buildings have garages underneath?

The listing on a gas oven is based upon a limited burn rate of no more than 4 hours within an 8 hour period combined with adequate ventilation. FYI, gas ovens DO make people sick. They don't have to kill to be a problem.

FYI, a TIFF 8800a is sensitive to methane only down to 500 ppm so it is not very useful for finding low level gas leaks and is cross-sensitive to about 30 common household compounds that can give false positives.

Perhaps if you took the NCI Carbon Monoxide and Combustion Certification Course you wouldn't be so cavalier with your responses.

Have a nice day,
Bob H.

Someone is crabby or is a stock holder in CO units from what I can tell.
Here is an code exemption in the Illinois law.
Section 20. Exemptions. The following residential units shall not require carbon monoxide detectors:
(1) A residential unit in a building that: (i) does not rely on combustion of fossil fuel for heat, ventilation, or hot water; (ii) is not connected in any way to a garage; and (iii) is not sufficiently close to any ventilated source of carbon monoxide, as determined by the local building commissioner, to receive carbon monoxide from that source.That makes total sense to you I should hope.
Telling me I have a cavalier attitude has nothing to do with the thread nor does pretending to be a pseudo intellectual as models and types of detectors has nothing to do with my statement so one can only guess you used it as an opening to impress us that you took a course and now are superior authority on the subject.....OK if you say so . :)

Perhaps you can stay to subject and not get so personal at 2;00 am as I can only guess the relatives drove you over the edge.

What you left out and is more important in the real world is that one should have a good CO detector within 6-10 feet from those vent-less fireplaces as people like to run them while sleeping .

Throw all the stats you want about them being technically safe but the new construction is built very tight and you should have a fresh air source.

Bob ...another thing you need to know is that much of my business is for Inspecting Condo buildings and perhaps you Inspect mainly single family homes with attached garages in an area with unreliable electric necessitating the need for power generators.

Condo Bob.

[Rick Taylor]

Hello all -

I'm a retired skipper off Merchant ships and have had plenty of experiences with all sorts of gas detectors. I've been reading this thread and wanted to ask for some help from the collective mind here regarding a situation I have which I would like to use a CO detector to monitor a space.

I have an oil fired furnace in the basement. I just upgraded it, so the unit is new, but the piping is original. There are a few more utilities down there, but not any sort of rec room, etc.

I've been reading up on the smart choice of low level CO detectors and have only seen 2 units mentioned, both of which need to be ordered from an obscure re-seller. Anyone here have any preferences for a particular unit or re-seller ?

Also, would any of you know of a remote low level detector, whereby I could have the alarm unit upstairs and the sensor down in the basement ? Which is what I'd really like to have.

Thanks !
Rick

[Roger Hankey]

Rick,

I refer you to CO (http://www.coexperts.com). for the low level detector.

[Charles Smith]

CO Emission Levels Appliance Combustion

Was it the turkey or the oven that put everyone to sleep???

There are new Carbon Monoxide requirements in Colorado. Revised State Statute 38-45-103 (Lofgren and Johnson Families Carbon Monoxide Safety Act) now requires that all existing single and multi-family dwellings offered for sale or transfer after July 1, 2009 have an operational Carbon Monoxide alarm installed.

I find many ovens that are emitting high CO levels (at the oven exhaust vent). I have found water heaters emitting over 2000 ppm. I always recommend installing CO Alarm.

I use Fyrite Model 60 Combustion Analyzer for measurements of gas appliances i.e. furnace, boiler, water heater and range / oven.

Carbon Monoxide testing is recommended for all atmospheric combustion appliances. Vented appliances may be measured two ways. “As Measured” is the reading without adjustments for oxygen content, sometimes referred to as ambient air.

“Air Free” is the read with adjustments for oxygen content. The burners of unvented gas ranges should be tested “As Measured”. The range ovens should be tested “Air Free”.

Oven manufacturers use 800 PPM (CO Air Free) as the upper limit for design and product testing.

The (As Measured) CO level can be deceiving. When (Excess Air) increases it dilutes the (As Measured) CO level. With a CO (as measured) meter “oven A” would not appear to be a problem.

Oven A
As-Measured CO = 18 ppm
Oxygen = 20%
Air-Free CO = 400 ppm

The (Air Free) CO measurement takes into account the (EA) and gives an oxygen free calculation.

Oven B
As-Measured CO = 209 ppm
Oxygen = 10%
Air-Free CO = 400 ppm
-------------------------------------------------------------------------
Rick Karg (R. J. Karg Associates) is the expert on testing

http://www.affordablecomfort.org/ima...ion_safety.pdf


Wisconsin Carbon Monoxide Protocol
http://www.doa.state.wi.us/docs_view2.asp?docid=2269

-------------------------------------------------------------------------
Building Performance Institute Protocol (04/2007)
http://www.bpi.org/documents/Gold_Sheet.pdf

1. Remove any items/foil in or on oven/range top
2. Make sure self-cleaning features are not activated
3. Test oven in vent sleeve, before dilution air
4. 100 ppm to 300 ppm (as measured) you must install a carbon monoxide detector and recommendation for service must be made to the consumer.

Greater than 300 ppm (as measured)—the unit must be serviced prior to work. If greater than 300 ppm after servicing, exhaust ventilation must be provided with a capacity of 25 CFM continuous or 100 CFM intermittent.

[DavidR]

I would be willing to bet that Rick Karg sat through one of Jim Davis' classes.
Being an expert on testing is one thing, being the man that wrote the book on CO testing is another. :)

Air free measurements are a calculated value that a combustion analyzer figures based on pre-programmed inputs and not 100% correct in calculation.
Unless you are verifying ANSI compliance with the appliance you are testing those readings don't have a lot meaning in the field.

[DavidR]

Oven manufacturers use 800 PPM (CO Air Free) as the upper limit for design and product testing.

The (As Measured) CO level can be deceiving. When (Excess Air) increases it dilutes the (As Measured) CO level. With a CO (as measured) meter “oven A” would not appear to be a problem.

Oven A
As-Measured CO = 18 ppm
Oxygen = 20%
Air-Free CO = 400 ppm

The (Air Free) CO measurement takes into account the (EA) and gives an oxygen free calculation.

Oven B
As-Measured CO = 209 ppm
Oxygen = 10%
Air-Free CO = 400 ppm





Which oven is safer?

Oven A or Oven B?

Both have a calculated value of 400 PPM air-free

[Charles Smith]

Both ovens should be serviced and a CO alarm installed.

The point is... if you use a CO meter that ONLY provides an "as measured" CO reading inside the oven exhaust vent ...you would think the oven is ok.

Read the protocols.

From Richard Karg, R.J. Karg Associates:
There are two scales with which to measure CO: one is “as-measured” and the other is “air-free.” As-measured is the method used by most technicians today. The CO is measured from a sample of combustion gases with no regard for the amount of excess air diluting the CO concentrations.
Excess air is the amount of air (specifically oxygen) in the combustion gases in excess of the exact amount needed for perfect combustion. When combustion is perfect, just the right amounts of fuel and oxygen are supplied to the combustion process so that all the oxygen is utilized—no oxygen remains in the combustion gases.
The basic problem with the as-measured method is this: As the amount of excess air increases, the as-measured CO value falls for a given source strength of CO. In other words, the amount of excess air in the sample can significantly influence the as-measured value. This can cause a technician to mistakenly think that a hazardous burner is working properly.

Air-free measurement of CO takes account of the amount of excess air by incorporating an adjustment to the as-measured ppm value, thus simulating air-free (oxygen-free) conditions in the combustion gases. To do this, a
reading of oxygen (O2) or carbon dioxide (CO2) percentage is taken from the combustion gases along with the as-measured CO reading. This can be done with a meter having the capability of measuring CO and O2 or CO2
percentage, or it can be done with two different meters, one measuring CO ppm and one measuring O2 or CO2 percentage.

[DavidR]

I would have to question where the readings were taken in Oven A as I don't think I've ever seen an oven run at 20% O2.

Oven B absolutely needs to be repaired as anything over 50 PPM as read being produced by an unvented appliance needs to be remedied.

The as read CO reading is the only reading you can trust when testing an appliance. It is what the appliance is producing at that point in time if combustion is stable the reading should not rise.
The air free number is only to ensure the appliance is within it's AGA/ANSI certification rating.

Advising those who are testing to disregard the as read value is not good advice IMHO.
I will take a measured value over a calculated one any day.

Might want to advise clients of the CO levels that any UL 2034 rated alarm is allowed to be exposed to before alarming as well.
They look at them very differently once they know how insensitive they are.